MAUNA KEA, Hawaii -- Two-and-a-half miles above sea level, David Monahan inches forward in the dark, popping open his cellphone to serve as an emergency flashlight. Nighttime temperatures have plunged below freezing. Snack food atop this dormant volcano consists of a bucket of dried squid.For Mr. Monahan and five fellow adventurers, this is bliss. They have slipped inside a dome at the W.M. Keck Observatory, home to two of the world's biggest optical telescopes. While astronomers prepare to search the skies, the newcomers shiver excitedly alongside celestial-imaging equipment, perched on a catwalk 75 feet off the ground. They look like stowaways on a space ship.The Bolshoi Azimuthal Telescope on Mount Pastukhov, a windy slope in the Russian Caucasus.Ordinarily, security guards would dash into the dome and eject such intruders. These visitors, however, have special privileges. Like Mr. Monahan, a hotel executive, each has donated $1,000 or more to the observatory, entitling them to an up-close glimpse of the frontiers of astronomy.Stargazing conjures up staid images of field trips to the local planetarium or puttering with a backyard telescope. But a new breed of obsessed fans is crisscrossing the globe to visit legendary observatories. Destinations include remote deserts, mountaintops -- even the South Pole.Many of these travelers are engineering buffs, people who love nothing more than to gawk at the one-of-a-kind quirks of multimillion-dollar machines. Even the smell of old telescopes' lubricants -- a bit like crayons -- intrigues them. Others are astronomy pilgrims retracing great moments in scientific history. Some simply like pioneering their own form of extreme travel.For observatories, affluent tourists can become welcome new funding sources. In Hawaii, the Keck has collected more than $6 million from private donors in the past few years to help pay for new instruments. Other sites regard steady visitor traffic as a good way to build up astronomy's image, particularly with school groups, which may include future scientists. Some popular sites get more than 100,000 visitors a year.One of the most ardent telescope tourists on the circuit is 47-year-old Louis Berman, who says he fell in love with stargazing as a boy. His passions turned to theater lighting as a young man before more job changes led him to become chief technology officer at a New York-based hedge fund. About seven years ago, Mr. Berman rekindled his infatuation with astronomy.

ASTRONOMICAL VIEWSFor a close encounter with galaxies far, far away, here are a few observatories to consider.Now he plans to visit one major observatory a month until he has enough material to write a book, which he plans to call "Scope Seeing." So far he has completed more than a dozen U.S. trips and is working on a European jaunt in August. His wife isn't too thrilled about his new hobby, he concedes, but if she doesn't want to come along, he travels alone."Visiting observatories is like going to a scientific church," Mr. Berman explains. "There's something wonderful about seeing stars that are so far away that you're looking back in time by billions of years."The longtime king of telescope tourism is William Keel, an astronomy professor at the University of Alabama. His adventures started in the 1980s, right after graduate school, during a research stint in Holland. He and his wife used their weekends to dash across Europe exploring old observatories, some dating back to the Renaissance. In Bonn, Germany, they saw the telescope that Friedrich Argelander used to compile the first major atlas of the stars in the mid-19th century. "It's almost mystical," Prof. Keel says. "You're in touch with this romantic legacy of the lone observer gazing into the sky."Prof. Keel has since trekked to observatories ranging from Chile to West Virginia. On his Web page (www.astr.ua.edu/keel/telescopes/1), he provides photos and chatty commentary about each stop, including his 1990 visit to Russia's Caucasus mountain range, home of the enormous -- but poorly engineered -- Bolshoi Azimuthal Telescope. Russian astronomers told him about a design quirk that made the Bolshoi, known as the Cyclops of the Caucasus, so elongated that it couldn't withstand strong winds. At one point astronomers there were forced to cover cracks in the telescope's mirror with black cloth in hopes of salvaging image quality.

'The Great Refractor'Amateurs are crisscrossing the world in search of stellar adventures, too. Some 200 of them belong to the Antique Telescope Society, which attracts engineers, woodworkers and casual historians. The ATS meets at a different observatory each year. This October the group will gather in Greenville, S.C., to see "The Great Refractor," a 125-year-old instrument that once belonged to Princeton University, and next year, it's off to Holland to celebrate the 400th anniversary of the invention of the telescope.For many members, old-fashioned craftsmanship is everything. "These older telescopes are controlled by amazing clockworks," says Peter Abrahams, an ATS member in Portland, Ore., who builds computer workstations.

The Yerkes Observatory in Williams Bay, Wis.One of Mr. Abrahams's favorites is at the Yerkes Observatory in Williams Bay, Wis. Completed in 1897, it was built in a gaudy Victorian style, with celestial and mythological figures rendered in ornate terra cotta inside and out. One of the last big telescopes to be built with lenses, rather than mirrors, to focus light, Yerkes was used for important scientific work until the 1980s. Academics hardly bother with it anymore, making it easier for amateur stargazers to use the instrument at night.Another ATS member, Walt Breyer, spent most of his career as a chemical engineer at Scott Paper Co., designing diapers and toilet-seat covers. Retired now, he says his growing interest in astronomy makes for better dinner-table chatter. Among his favorite tales: visiting Birr Castle in Northern Ireland, home of a huge, 19th-century telescope, and staying for dinner with Lord Rosse, whose forebears built the observatory."There we were in sweatshirts and other casual clothes, suitable to explore the telescope, having dinner in the castle," Mr. Breyer recalls. "I wonder what Lord Rosse and his wife thought of the Americans who came to dinner so casually dressed."Modern facilities usually aren't as obliging. Visitors' galleries provide daytime glimpses of some equipment, but doors are generally locked at night so that astronomers can work without distractions. An extreme case in point is the South Pole Observatory, funded by the National Science Foundation. Created in 1957, it hosts as many as 200 visiting astronomers at a time. Scientists there study submillimeter radiation from stars, which usually is obscured by water vapor in the earth's atmosphere. Visibility improves at the South Pole, however, thanks to the extremely cold, dry air.Travelers who stop by for a quick tour might get a cup of coffee or a meal -- but that's all, says D.A. Harper, a former director of the Center for Astrophysical Research in Antarctica, where he oversaw the South Pole outpost. "Space is very tight," Prof. Harper explains. "The rule is, if they want to spend the night, they've got to bring their own tent."

Star Party, $600That frosty welcome -- plus the $40,000 round-trip cost of flying to the Pole from the Antarctic coast -- has kept unplanned tourist traffic down to 10 guests or fewer most years, Prof. Harper says. Still, a few teachers, journalists and politicians who make the trip each year get friendlier treatment, as part of the NSF's outreach efforts. Arlene Sharp, a Chicago educator, spent six days at the South Pole Observatory in 1996 with a middle-school student. She says she has been sharing her experiences with teachers and parents ever since.A technician at the W.M. Keck Observatory, inspecting the laser guide star beam on the K2 telescope.In Texas' Big Bend region, the McDonald Observatory offers tourists a pragmatic compromise. Nighttime access to its largest telescopes is highly restricted. But for $600, the observatory will throw a private "Star Party," letting guests spend hours gazing at planets, nebulae and distant galaxies through three of its smaller scopes."Being out there is elemental, wild and simple," says Mike Halperin, a Seattle-area doctor, who took such a trip in April. He was especially moved by up-close views of Saturn's rings.Some of his friends on the trip were ex-Microsoft Corp. employees who had hoped to see one of their former colleagues, Charles Simonyi, orbiting the earth during his brief stint as an astronaut. No luck. Mr. Simonyi's spaceship was in too low an orbit to be visible. But other spectacular attractions, such as globular star clusters, made up for it.In Hawaii, about 100,000 visitors a year come to a viewing station partway up the slopes of Mauna Kea, where they can see the night stars through relatively small telescopes. About 25,000 make it to the 13,796-foot summit, usually for a daytime look at the Keck and eight other major observatories operated by European, Japanese and North American universities.As for getting inside the Keck at night, that's a rarer experience afforded only about 60 major donors a year. On such trips, the observatory's development officer, Debbie Goodwin, cheerfully barges through doors marked "No Visitors," her guests in tow. A popular stop is the "mirror barn," where the observatory stores spare hexagonal tiles for the Keck's two, 32.8-foot primary mirrors. The 4-inch-thick tiles are polished to within one-millionth of an inch of design specifications and cost more than $800,000 apiece. Visitors can't touch them, but no one stops people from cavorting in front of them, watching their reflections as they giggle and make faces.To some visitors' surprise, there aren't any chances to see actual stars through the Keck's main telescope. Images are captured digitally, turned into columns of numbers -- and transmitted to astronomers at computer stations miles away. That helps researchers do their work more efficiently, but it creates a sightseeing experience that isn't much different than watching bond traders adjust their portfolios.

Into Thin AirThere are other stops on the tour that are crowd pleasers, however. One involves a thin orange laser beam that's shot into the sky, helping the Keck's telescope produce images so clear they rival those of the Hubble Space Telescope.The thin air atop Mauna Kea reduces the sort of atmospheric distortion that makes stars twinkle, but doesn't eliminate it altogether. Fancy computer software can correct for this, as long as astronomers are able to calibrate their adjustments on a precisely defined object in the heavens.Thus the laser. Its thin orange beam excites atoms in the upper atmosphere, creating a disk-shaped image that's 60 miles away -- and just 20 inches wide. Software analyzes that artificial "star" and makes adjustments until its image is as crisp as possible. This tinkering, known as adaptive optics, greatly sharpens the images of celestial objects.As the orange streak lights up the Hawaiian sky one evening, visitors inside the dome involuntarily lift up their arms and point to it. They try to guess how far out it can be tracked -- a mile? two miles? -- before it disappears into the infinity of space.Among the most delighted spectators is Clive Davies, the retired president of Linear Technologies Inc., a Silicon Valley chip company. Forty years earlier, he was a graduate student in physics, curious about all kinds of things, but it's been a long time since he has thought about lasers, optics and the heavens. Now he's enjoying the chance to revisit that part of his life -- so much so that he has donated more than $20,000 to the Keck in the past few years."It keeps the gray cells active," Mr. Davies says.

Astronomical ViewsFor a close encounter with galaxies far, far away, here are a few observatories to consider:NAME/LOCATIONHOURS/WEB SITECOMMENTPalomar Observatory Palomar Mountain, Calif.open daily, 9 a.m. to 4 p.m., no nighttime hours; free; www.astro.caltech.edu3Edwin Hubble worked here. Completed in 1949 and formerly the world's biggest optical telescope, it took 21 years -- and much turmoil -- to build. Within driving distance of Disneyland.Royal Observatory Greenwich Greenwich, England10 a.m. to 5 p.m. daily; free; evening stargazing for private parties; www.rog.nmm.ac.uk4Founded in 1675; the Prime Meridian that separates Eastern and Western longitude runs through the middle of the site. Visitors can put one foot in each half of the world.U.S. Naval Observatory Washington, D.C.limited evening tours; must book 4-6 weeks in advance; free; www.usno.navy.mil5Founded in 1830; an astronomer here discovered the two satellites of Mars in 1877. The official source of time for the Global Positioning System.Southern African Large Telescope Sutherland, South Africaopen Mon.-Sat.; day and evening tours; advanced booking required; about $3-$5 www.salt.ac.za6Daytime visitors can see a newly constructed, 11-meter optical telescope that is being readied for scientific use. Nighttime guests are limited to two smaller, visitors' telescopes.Very Large Array Socorro, N.M.open daily, 8:30 a.m. to dusk; free; www.vla.nrao.edu7This is a cluster of 27 radio antennas, each more than 80 feet wide, spread across the desert, listening to the sounds of outer space.